Multilayer detergent tablet with different hardness

ABSTRACT

The present invention relates to a detergent tablet having at least a first and a second layer, whereby the first layer is softer than the second layer, and if said tablet has more than two layers, the tablet is such that a softer layer is situated at an end of the tablet to increase the integrity and robustness of the entire tablet during production, shipping and handling while keeping substantially good dispensing properties.

The present invention relates to detergent tablets, especially thoseadapted for use in washing.

Although cleaning compositions in tablet form have often been proposed,these have not (with the exception of soap bars for personal washing)gained any substantial success, despite the several advantages ofproducts in a unit dispensing form. One of the reasons for this may bethat detergent tablets usually dissolve slower than the constituentpowders from which they are made, simply because the constituent powdersare forced close together in the tablet, with comparatively littleopportunity for water to permeate between them. This gives rise to theproblem that slow dissolving tablets cause residues which may forexample be visible through the door of the washing machine during thewash cycle, or which stick to the fabrics at the end of the wash cycle,or both. This may be compensated by using low compression forces to keephigh porosity and good dissolution profile. However, such tablets aretypically softer and have mechanical characteristics such that breakageis likely to occur during production or handling.

DE-A-2 207 633, published on the 30^(th) of August 1973, disclosestablets having three layers, the middle layer being sandwiched betweentwo end layers, the two end layers being made so as to protect themiddle layers from mechanical shocks, while allowing tablet dissolutionin less than a minute.

However, particularly in certain front loading washing machines,problems of tablet residues appearing visibly at the window of thewashing machine have still been encountered. Indeed, in particular fordetergent tablets, the dissolution problems are particularly acute, duefor example to the tendency of gelling of the surfactant materials, orto low level of water used for environmental reasons, or due todissolution at low temperature, etc.

The object of the present invention is to provide detergent tabletstypically formed by compressing a particulate material, the tablet beingsuitable for storing, shipping and handling without breakage whiledissolving easily and rapidly in wash solution, releasing the activeingredients into the wash solution and completely disintegrating anddispersing in alkaline or surfactant-rich solutions such as the washliquor.

SUMMARY OF THE INVENTION

The object of the invention is achieved by providing a detergent tablethaving at least a first and a second layer, whereby the first layer issofter than the second layer, and if said tablet has more than twolayers, the tablet is such that a softer layer is situated at an end ofthe tablet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents two typical profiles for measuring the elasticity of alayer or of a tablet.

FIG. 2 represents a typical profile for measuring the elasticity of alayer or of a tablet.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents two typical profiles for measuring the elasticity of alayer or of a tablet, the profile representing the load applied to thetablet or layer, corresponding to the resistance of the tablet or layer,in function of the displacement of the load along the main axis of thetablet or layer. A curve corresponding to a more elastic and to a lesselastic tablet or layer are shown, together with schematics showing thestructural changes to which the tablet or layer is submitted during themeasurement.

FIG. 2 represents a typical profile for measuring the elasticity of alayer or of a tablet, the profile representing the load applied to thetablet or layer, corresponding to the resistance of the tablet or layer,in function of the displacement of the load along the main axis of thetablet or layer. The breaking point giving the maximum height H of thecurve is marked, as well as the area A under the curved taken from thebreaking point, whereby the elasticity is deduced from this by dividingA by H.

The invention relates to a detergent tablet. By detergent, it is meantthat the tablet comprises surfactants. A tablet is defined as having aheight along a main axis and a cross section normal to the main axis,the cross section being preferably substantially constant whentravelling along the main axis, the tablet having two ends, each endbeing situated at each end of the main axis and having a surface areasubstantially equal to the cross section of the tablet.

The tablet is such that it comprises at least a first and a secondlayer. Normally, these layers are produced by compression of particulatematerials. Composition of these layers may be similar or different, andcompression force used for forming these layers may also be similar ordifferent. It should be noted that a preferred embodiment of a tabletaccording to the invention comprises only two layers, but tablets withmore layers may be considered.

According to the invention, a layer is preferably a part of a tabletmade from compressing particulate materials, this part of the tablethaving a height along the main axis of the tablet and a cross sectioncorresponding to the cross section of the tablet, such that thecomposition or the physical and mechanical characteristics of this partdiffers from the rest of the tablet. In other words, a tablet accordingto the invention is made by piling up layers along the main axis to formthe tablet, this layers adhering to each other to form the tablet,adhesion between layers being provided by mechanical or chemical means.Taken independently, each layer may be considered as a mono-layertablet, as far as composition is concerned, for example.

According to the invention, the first layer is softer than the secondlayer. By softer, it should be understood that the tensile strength islower than the tensile strength of the second layer. When more than twolayers are present in the tablet, a softer layer is simply a layer suchthat there is another layer in the tablet which is less soft. In otherwords, if three layers are present with gradual and different softness,there are two softer layers. According to the invention, the softestlayer is the layer most soft among all layers in the tablet. Sameapplies for harder, i.e. less soft, or hardest, i.e. least soft.Typically, the softer layer has a tensile strength 10% lower than thetensile strength of a harder layer part of the same tablet, preferably20% lower, more preferably 30% lower, even more preferably 40% lower andmost preferably 50% lower. According to the invention, thesoftness-hardness scale is measured by the tensile strength of thetablet.

According to the invention, if said tablet has more than two layers, thetablet is such that a softer layer is situated at an end of the tablet.The softer layer is not necessarily the softest layer. In a preferredembodiment, the softest layer is situated at one end. This is beneficialto dissolution because the surface activity of this soft layer is highbecause it is exposed as it is situated at one end. Indeed, according tothe invention, the mechanical properties and the dissolution propertiesof a single tablet can be rendered more independent the ones from theothers, so that a harder layer will more specifically provide mechanicalintegrity and protection while a softer layer will more specificallyfavour fast and efficient dissolution.

The level of softness of different layers may be set using differentparameters, such as different chemical composition, or differentcompression force. In particular, if using different compositions, alayer may comprise more binders than another one to be made harder, i.e.less soft. It should be noted that it is preferred that a softer layercomprises higher levels of surfactant per weight. Indeed, a softer layerwill more readily dissolve, and therefore will compensate gelling ofsurfactants by its softness. Indeed, gelling of surfactant is hinderingfast and effective dissolution, which can be compensated byconcentrating such surfactants in a softer layer. This can beadvantageously combined with use of highly soluble compounds, hydrotropecompounds, and compounds providing high cohesive effect at lowercompression force, for example.

In another preferred embodiment and in a two layer tablet according tothe invention, the tablet is such that the less soft layer is situatedat an end of the tablet. Indeed, it was found sufficient to obtain goodmechanical characteristics to have one harder layer at one end of thetablet. This particularly applies to the method for making a tabletaccording to the invention, whereby the less soft layer of the tablet isplaced at the bottom end of the tablet during production. Even morepreferably, the least soft layer is placed at the bottom end of thetablet during production. Indeed, mechanical stress is particularly highduring production, and almost only the bottom end of the tablet isexposed to mechanical constraints at this stage. Furthermore, thisallows to obtain good mechanical resistance while allowing to place asofter layer at the other end of the tablet, whereby this softer layerwill benefit of a higher surface of contact with solution whendissolving the tablet in solution.

Such mechanical resistance was found to be improved when using a tablethaving a substantially rectangular cross section. Indeed, solidity ofthe tablet could be improved at constant compression value by using arectangular tablet. At equal weight, equal compression force, equalcomposition, equal height and equal volume, rectangular tablet have amechanical resistance significantly improved when compared to roundtablets. This particularly applies to square tablets.

A layer may preferably have a height varying between 5 and 95% of thetotal tablet height. More preferably, the harder the layer is, thethinner it is to have a minimum impact on the overall dissolution of theentire tablet.

Typically, a two layer tablet according to the invention will comprise asoft layer having a tensile strength between 5 and 100 kPa, whereas thehard layer is having a tensile strength comprised between 5.5 and 150kPa.

Elasticity

In a preferred embodiment according to the invention, the tabletcomprises at least two layers having a different elasticity, the moreelastic layer being more resistant to mechanical shocks, the morebrittle layer having better dissolution characteristics. Indeed, a lesselastic layer, thereby more brittle, will disperse readily in solution.In a most preferred embodiment, according to the invention, a softerlayer is also a more brittle layer, and a harder layer is also moreelastic. However, this may not be the case.

The elasticity of a tablet or of a layer from a tablet is evaluated asfollows:

1—A load is pressed flat onto one end of the tablet or layer for whichthe elasticity is tested, the load being pressed along the direction ofthe main axis of the tablet or layer.

2—The force by the load is measured in function of the displacement ofthe load.

3—Two possible curves obtained by this method are illustrated in FIG. 1.

These two curves are showing the type of curves obtained for twodifferent tablets or layers, one of the tablet being more elastic thanthe other, which in turn is more brittle (=less elastic). The elasticityvalue corresponding to the tablet or layer tested is deduced from thisexperimental curve as follows:

The area under the curve and beyond the breaking point is calculated byintegrating the curve from its top value up to large displacementvalues. This area A is then divided by the height H of the curve at thebreaking point for normalising the elasticity of the tablet or layer, E.This is illustrated in FIG. 2.

High values for E represent high elasticity, while low value representhighly brittle layers or tablets.

In order to achieve this test, the following equipment was used:

Instron 4444 series machine tester with a standard load cell of 2 kNlinked to a normal PC computer. The program used to make thecalculations was a Series IX version 7.49.00 provided by the equipmentsupplier.

A Plexiglas cylinder of 25 mm diameter, 30 mm height and a weight of 18gr. was used to crush the tablet or layer.

A standard dye to make tablets or layers, this dye having a of 54 mmdiameter.

the tablet or layer is placed between the plates of the Instron 4444 andthe Plexiglas cylinder is placed in the middle of the tablet or layerend.

The cross head of the load cell moves at a constant speed of 10 mm/minand the computer starts to record the force of resistance of the tabletversus the displacement of the cylinder into the tablets.

The elasticity is calculated by dividing the area under the slope afterthe breakage point by its maximum height (see figures and explanationsabove).

The elasticity is hereby measured in J/kN (Joules for the area and kNfor the maximum height used to normalise the area curves).

Typically, the elasticity value for a preferred embodiment of tabletsaccording to the invention and more particularly adapted for laundry useis comprised between 0.5 and 5 J/kN, and more preferably between 1 and 4J/kN. It is preferred that a more elastic layer or tablet for laundryuse, for example, has an elasticity comprised between 3 and 4J/kN, morepreferably between 3.1 and 3.5 J/kN. It is preferred that a more brittlelayer or tablet for laundry use, for example, has an elasticitycomprised between 1.5 and 2.5 J/kN, more preferably between 1.7 and 2.1J/kN.

Highly Soluble Compounds

In a preferred embodiment, the tablet preferably comprises a highlysoluble compound. More preferably, this compound is comprised or ispresent at higher levels per weight in the relatively hard layer of thetablet, i.e. the less soft layer, in order to further favourdissolution. Indeed, it may be preferred to aid dissolution of theharder layer, as this layer will for example be more compressed than asofter layer. Such a compound could be formed from a mixture or from asingle compound. A highly soluble compound is defined as follow:

A solution is prepared as follows comprising de-ionised water as well as20 grams per liter of a specific compound:

1—20 g of the specific compound is placed in a Sotax Beaker. This beakeris placed in a constant temperature bath set at 10° C. A stirrer with amarine propeller is placed in the beaker so that the bottom of thestirrer is at 5 mm above the bottom of the Sotax beaker. The mixer isset at a rotation speed of 200 turns per minute.

2—980 g of the de-ionised water is introduced into the Sotax beaker.

3—10 s after the water introduction, the conductivity of the solution ismeasured, using a conductivity meter.

4—Step 3 is repeated after 20, 30, 40, 50, 1min, 2 min, 5 min and 10 minafter step 2.

5—The measurement taken at 10 min is used as the plateau value ormaximum value.

The specific compound is highly soluble according to the invention whenthe conductivity of the solution reaches 80% of its maximum value inless than 10 seconds, starting from the complete addition of thede-ionised water to the compound. Indeed, when monitoring theconductivity in such a manner, the conductivity reaches a plateau aftera certain period of time, this plateau being considered as the maximumvalue. Such a compound is preferably in the form of a flowable materialconstituted of solid particles at temperatures comprised between 10 and80° Celsius for ease of handling, but other forms may be used such as apaste or a liquid.

Example of highly soluble compounds include Sodium di isoalkylbenzenesulphonate or Sodium toluene sulphonate.

Cohesive Effect

In a preferred embodiment of this invention, the tablet preferablycomprises a compound having a Cohesive Effect on the particulatematerial of a detergent matrix forming the tablet. More preferably, thiscompound is comprised or is present at higher levels per weight in therelatively hard layer of the tablet, i.e. the less soft layer, in orderto obtain satisfactory hardness without need for high compression. TheCohesive Effect on the particulate material of a detergent matrixforming the tablet or a layer of the tablet is characterised by theforce required to break a tablet or layer based on the examineddetergent matrix pressed under controlled compression conditions. For agiven compression force, a high tablet or layer strength indicates thatthe granules stuck highly together when they were compressed, so that astrong cohesive effect is taking place. Means to assess tablet or layerstrength (also refer to diametrical fracture stress) are given inPharmaceutical dosage forms: tablets volume 1 Ed. H. A. Lieberman et al,published in 1989.

The cohesive effect is measured by comparing the tablet or layerstrength of the original base powder without compound having a cohesiveeffect with the tablet or layer strength of a powder mix which comprises97 parts of the original base powder and 3 parts of the compound havinga cohesive effect. The compound having a cohesive effect is preferablyadded to the matrix in a form in which it is substantially free of water(water content below 10% (pref. below 5%)). The temperature of theaddition is between 10 and 80 C, more pref. between 10 and 40 C.

A compound is defined as having a cohesive effect on the particulatematerial according to the invention when at a given compacting force of3000 N, tablets with a weight of 50 g of detergent particulate materialand a diameter of 55 mm have their tablet tensile strength increased byover 30% (preferably 60 and more preferably 100%) by means of thepresence of 3% of the compound having a cohesive effect in the baseparticulate material.

An example of a compond having a cohesive effect is Sodium diisoalkylbenzene sulphonate.

When integrating a highly soluble compound having also a cohesive effecton the particulate material used for a tablet or layer formed bycompressing a particulate material comprising a surfactant, thedissolution of the tablet or layer in an aqueous solution issignificantly increased. In a preferred embodiment, at least 1% perweight of a tablet or layer is formed from the highly soluble compound,more preferably at least 2%, even more preferably at lest 3% and mostpreferably at least 5% per weight of the tablet or layer being formedfrom the highly soluble compound having a cohesive effect on theparticulate material.

It should be noted that a composition comprising a highly solublecompound as well as a surfactant is disclosed in EP-A0 524 075, thiscomposition being a liquid composition.

A highly soluble compound having a cohesive effect on the particulatematerial allows to obtain a tablet having a higher tensile strength atconstant compacting force or an equal tensile strength at lowercompacting force when compared to traditional tablets. Typically, awhole tablet will have a tensile strength of more than 5 kPa, preferablyof more than 10 kPa, more preferably, in particular for use in laundryapplications, of more than 15 kPa, even more preferably of more than 30kPa and most preferably of more than 50 kPa, in particular for use indish washing or auto dish washing applications; and a tensile strengthof less than 300 kPa, preferably of less than 200 kPa, more preferablyof less than 100 kPa, even more preferably of less than 80 kPa and mostpreferably of less than 60 kPa. Indeed, in case of laundry application,the tablets should be less compressed than in case of auto dish washingapplications for example, whereby the dissolution is more readilyachieved, so that in a laundry application, the tensile strength ispreferably of less than 30 kPa.

This allows to produce tablets or layers which have a solidity andmechanical resistance comparable to the solidity or mechanicalresistance of traditional tablets while having a less compact tablet orlayer thus dissolving more readily.

Furthermore, as the compound is highly soluble, the dissolution of thetablet or layer is further facilitated, resulting in a synergy leadingto facilitated dissolution for a tablet according to the invention.

Tablet Manufacture

For the purpose of manufacture of a single layer, the layer may beconsidered as a tablet itself.

Detergent tablets of the present invention can be prepared simply bymixing the solid ingredients together and compressing the mixture in aconventional tablet press as used, for example, in the pharmaceuticalindustry. Preferably the principal ingredients, in particular gellingsurfactants, are used in particulate form. Any liquid ingredients, forexample surfactant or suds suppressor, can be incorporated in aconventional manner into the solid particulate ingredients. Inparticular for laundry tablets, the ingredients such as builder andsurfactant can be spray-dried in a conventional manner and thencompacted at a suitable pressure. Preferably, the tablets according tothe invention are compressed using a force of less than 100000 N, morepreferably of less than 50000 N, even more preferably of less than 5000N and most preferably of less than 3000 N. Indeed, the most preferredembodiment is a tablet suitable for laundry compressed using a force ofless than 2500 N, but tablets for auto dish washing may also beconsidered for example, whereby such auto dish washing tablets areusually more compressed than laundry tablets.

The particulate material used for making the tablet of this inventioncan be made by any particulation or granulation process. An example ofsuch a process is spray drying (in a co-current or counter current spraydrying tower) which typically gives low bulk densities 600 g/l or lower.Particulate materials of higher density can be prepared by granulationand densification in a high shear batch mixer/granulator or by acontinuous granulation and densification process (e.g. using Lodige® CBand/or Lodige® KM mixers). Other suitable processes include fluid bedprocesses, compaction processes (e.g. roll compaction), extrusion, aswell as any particulate material made by any chemical process likeflocculation, crystallisation sentering, etc. Individual particles canalso be any other particle, granule, sphere or grain.

The components of the particulate material may be mixed together by anyconventional means. Batch is suitable in, for example, a concrete mixer,Nauta mixer, ribbon mixer or any other. Alternatively the mixing processmay be carried out continuously by metering each component by weight onto a moving belt, and blending them in one or more drum(s) or mixer(s).Non-gelling binder can be sprayed on to the mix of some, or all of, thecomponents of the particulate material. Other liquid ingredients mayalso be sprayed on to the mix of components either separately orpremixed. For example perfume and slurries of optical brighteners may besprayed. A finely divided flow aid (dusting agent such as zeolites,carbonates, silicas) can be added to the particulate material afterspraying the binder, preferably towards the end of the process, to makethe mix less sticky.

The tablets may be manufactured by using any compacting process, such astabletting, briquetting, or extrusion, preferably tabletting. Suitableequipment includes a standard single stroke or a rotary press (such asCourtoy®, Korch®, Manesty®, or Bonals®). The tablets prepared accordingto this invention preferably have a diameter of between 20 mm and 60 mm,preferably of at least 35 and up to 55 mm, and a weight between 25 and100 g. The ratio of height to diameter (or width) of the tablets ispreferably greater than 1:3, more preferably greater than 1:2. Thecompaction pressure used for preparing these tablets need not exceed100000 kN/m², preferably not exceed 30000 kN/m², more preferably notexceed 5000 kN/m², even more preferably not exceed 3000 kN/m² and mostpreferably not exceed 1000 kN/m². In a preferred embodiment according tothe invention, the tablet has a density of at least 0.9 g/cc, morepreferably of at least 1.0 g/cc, and preferably of less than 2.0 g/cc,more preferably of less than 1.5 g/cc, even more preferably of less than1.25 g/cc and most preferably of less than 1.1 g/cc.

Multi layered tablets are typically formed in rotating presses byplacing the matrices of each layer, one after the other in matrix forcefeeding flasks. As the process continues, the matrix layers are thenpressed together in the pre-compression and compression stages stationsto form the multilayer layer tablet. With some rotating presses it isalso possible to compress the first feed layer before compressing thewhole tablet.

Hydrotrope Compound

In a preferred embodiment of the invention, a highly soluble compoundhaving a cohesive effect is integrated to the tablet of the invention,whereby this compound is also a hydrotrope compound. Such hydrotropecompound may be generally used to favour surfactant dissolution byavoiding gelling, so that they may be for example advantageouslycomprised in a softer layer. A specific compound is defined as beinghydrotrope as follows (see S. E. Friberg and M. Chiu, J. DispersionScience and Technology, 9(5&6), pages 443 to 457, (1988-1989)):

1. A solution is prepared comprising 25% by weight of the specificcompound and 75% by weight of water.

2. Octanoic Acid is thereafter added to the solution in a proportion of1.6 times the weight of the specific compound in solution, the solutionbeing at a temperature of 20° Celsius. The solution is mixed in a Sotaxbeaker with a stirrer with a marine propeller, the propeller beingsituated at about 5 mm above the bottom of the beaker, the mixer beingset at a rotation speed of 200 rounds per minute.

3. The specific compound is hydrotrope if the the Octanoic Acid iscompletely solubilised, i.e. if the solution comprises only one phase,the phase being a liquid phase.

It should be noted that in a preferred embodiment of the invention, thehydrotrope compound is a flowable material made of solid particles atoperating conditions between 15 and 60° Celsius.

Hydrotrope compounds include the compounds listed thereafter:

A list of commercial hydrotropes could be found in McCutcheon'sEmulsifiers and Detergents published by the McCutcheon division ofManufacturing Confectioners Company. Compounds of interest also include:

1. Nonionic hydrotrope with the following structure:

where R is a C8-C10 alkyl chain, x ranges from 1 to 15, y from 3 to 10.

2. Anionic hydrotropes such as alkali metal aryl sulfonates. Thisincludes alkali metal salts of benzoic acid, salicylic acid,bezenesulfonic acid and its many derivatives, naphthoic acid and varioushydroaromatic acids. Examples of these are sodium, potassium andammonium benzene sulfonate salts derived from toluene sulfonic acid,xylene sulfonic acid, cumene sulfonic acid, tetralin sulfonic acid,naphtalene sulfonic acid, methyl-naphtalene sulfonic acid, dimethylnaphtalene sulfonic acid, trimethyl naphtalene sulfonic acid=Otherexamples include salts of dialkyl benzene sulfonic acid such as salts ofdi-isopropyl benzene sulfonic acid, ethyl methyl benzene sulfonic acid,alkyl benzene sulfonic acid with an alkyl chain length with 3 to 10,(pref. 4 to 9), linear or branched alkyl sulfonates with an alkyl chainwith 1 to 18 carbons.

3. Solvent hydrotropes such as alkoxylated glycerines and alkoxylatedglycerides, esters slakoxylated glycerines, alkoxylated fatty acids,esters of glycerin, polyglycerol esters. Preferred alkoxylatedglycerines have the following structure:

where l, m and n are each a number from 0 to about 20, with l+m+n=fromabout 2 to about 60, preferably from about 10 to about 45 and Rrepresents H, CH₃ or C₂H₅

Preferred alkoxylated glycerides have the following struture

where R1 and R2 are each C_(n)COO or —(CH2CHR₃—O)_(l)—H where R₃=H, CH₃or C₂H₅ and l is a number from 1 to about 60, n is a number from about 6to about 24.

4. Polymeric hydrotropes such as those described in EP636687:

where E is a hydrophilic functional group,

R is H or a C1-C10 alkyl group or is a hydrophilic functional group;

R1 is H a lower alkyl group or an aromatic group,

R2 is H or a cyclic alkyl or aromatic group.

The polymer typically has a molecular weight of between about 1000 and1000000.

5. Hydrotrope of unusual structure such as5-carboxy-4-hexyl-2-cyclohexene-1-yl octanoic acid (Diacid®)

Use of such compound in the invention would further increase thedissolution rate of the tablet, as a hydrotrope compound facilitatesdissolution of surfactants, for example. Such a compound could be formedfrom a mixture or from a single compound.

Coating

Solidity of the tablet according to the invention may be furtherimproved by making a coated tablet, the coating covering a non-coatedtablet according to the invention, thereby further improving themechanical characteristics of the tablet while maintaining or furtherimproving dissolution.

This very advantageously applies to multi-layer tablets according to theinvention, whereby the mechanical characteristics of a harder layer canbe transmitted via the coating to the rest of the tablet, thus combiningthe advantage of the coating with the advantage of the harder layer.Indeed, mechanical constraints will be transmitted through the coating,thus improving mechanical integrity of the tablet.

In one embodiment of the present invention, the tablets may then becoated so that the tablet does not absorb moisture, or absorbs moistureat only a very slow rate. The coating is also strong so that moderatemechanical shocks to which the tablets are subjected during handling,packing and shipping result in no more than very low levels of breakageor attrition. Finally the coating is preferably brittle so that thetablet breaks up when subjected to stronger mechanical shock.Furthermore it is advantageous if the coating material is dissolvedunder alkaline conditions, or is readily emulsified by surfactants. Thiscontributes to avoiding the problem of visible residue in the window ofa front-loading washing machine during the wash cycle, and also avoidsdeposition of undissolved particles or lumps of coating material on thelaundry load.

Water solubility is measured following the test protocol of ASTME1148-87 entitled, “Standard Test Method for Measurements of AqueousSolubility”.

Suitable coating materials are dicarboxylic acids. Particularly suitabledicarboxylic acids are selected from the group consisting of oxalicacid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelicacid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid,dodecanedioic acid, tridecanedioic acid and mixtures thereof.

The coating material has a melting point preferably of from 40° C. to200° C.

The coating can be applied in a number of ways. Two preferred coatingmethods are a) coating with a molten material and b) coating with asolution of the material.

In a), the coating material is applied at a temperature above itsmelting point, and solidifies on the tablet. In b), the coating isapplied as a solution, the solvent being dried to leave a coherentcoating. The substantially insoluble material can be applied to thetablet by, for example, spraying or dipping. Normally when the moltenmaterial is sprayed on to the tablet, it will rapidly solidify to form acoherent coating. When tablets are dipped into the molten material andthen removed, the rapid cooling again causes rapid solidification of thecoating material. Clearly substantially insoluble materials having amelting point below 40° C. are not sufficiently solid at ambienttemperatures and it has been found that materials having a melting pointabove about 200° C. are not practicable to use. Preferably, thematerials melt in the range from 60° C. to 160° C., more preferably from70° C. to 120° C.

By “melting point” is meant the temperature at which the material whenheated slowly in, for example, a capillary tube becomes a clear liquid.

A coating of any desired thickness can be applied according to thepresent invention. For most purposes, the coating forms from 1% to 10%,preferably from 1.5% to 5%, of the tablet weight.

The tablet coatings of the present invention are very hard and provideextra strength to the tablet.

In a preferred embodiment of the present invention the fracture of thecoating in the wash is improved by adding a disintegrant in the coating.This disintegrant will swell once in contact with water and break thecoating in small pieces. This will improve the dissolution of thecoating in the wash solution. The disintegrant is suspended in thecoating melt at a level of up to 30%, preferably between 5% and 20%,most preferably between 5 and 10% by weight. Possible disintegrants aredescribed in Handbook of Pharmaceutical Excipients (1986). Examples ofsuitable disintegrants include starch: natural, modified orpregelatinized starch, sodium starch gluconate; gum: agar gum, guar gum,locust bean gum, karaya gum, pectin gum, tragacanth gum; croscarmyloseSodium, crospovidone, cellulose, carboxymethyl cellulose, algenic acidand its salts including sodium alginate, silicone dioxide, clay,polyvinylpyrrolidone, soy polysacharides, ion exchange resins andmixtures thereof.

Tensile Strength

For the purpose of measuring tensile strength of a layer, the layer maybe considered as a tablet itself.

Depending on the composition of the starting material, and the shape ofthe tablets, the used compacting force may be adjusted to not affect thetensile strength, and the disintegration time in the washing machine.This process may be used to prepare homogenous or layered tablets of anysize or shape.

For a cylindrical tablet, the tensile strength corresponds to thediametrical fracture stress (DFS) which is a way to express the strengthof a tablet or layer, and is determined by the following equation:

Tensile strength=2 F/πDt

Where F is the maximum force (Newton) to cause tensile failure(fracture) measured by a VK 200 tablet hardness tester supplied by VanKell industries, Inc. D is the diameter of the tablet or layer, and tthe thickness of the tablet or layer. For a non round tablet, πD maysimply be replaced by the perimeter of the tablet.

(Method Pharmaceutical Dosage Forms: Tablets Volume 2 Page 213 to 217).A tablet having a diametral fracture stress of less than 20 kPa isconsidered to be fragile and is likely to result in some broken tabletsbeing delivered to the consumer. A diametral fracture stress of at least25 kPa is preferred.

This applies similarly to non cylindrical tablets, to define the tensilestrength, whereby the cross section normal to the height of the tabletis non round, and whereby the force is applied along a directionperpendicular to the direction of the height of the tablet and normal tothe side of the tablet, the side being perpendicular to the non roundcross section.

Tablet Dispensing

The rate of dispensing of a detergent tablet can be determined in thefollowing way:

Two tablets, nominally 50 grams each, are weighed, and then placed inthe dispenser of a Baucknecht® WA9850 washing machine. The water supplyto the washing machine is set to a temperature of 20° C. and a hardnessof 21 grains per gallon, the dispenser water inlet flow-rate being setto 8 l/min. The level of tablet residues left in the dispenser ischecked by switching the washing on and the wash cycle set to washprogram 4 (white/colors, short cycle). The dispensing percentage residueis determined as follows:

% dispensing=residue weight×100/original tablet weight

The level of residues is determined by repeating the procedure 10 timesand an average residue level is calculated based on the ten individualmeasurements. In this stressed test a residue of 40% of the startingtablet weight is considered to be acceptable. A residue of less than 30%is preferred, and less than 25% is more preferred.

It should be noted that the measure of water hardness is given in thetraditional “grain per gallon” unit, whereby 0.001 mole per liter=7.0grain per gallon, representing the concentration of Ca²⁺ ions insolution.

Effervescent

In another preferred embodiment of the present invention the tabletsfurther comprises an effervescent.

Effervescency as defined herein means the evolution of bubbles of gasfrom a liquid, as the result of a chemical reaction between a solubleacid source and an alkali metal carbonate, to produce carbon dioxidegas,

i.e. C₆H₈O₇+3NaHCO₃→Na₃C₆H₅O₇+3CO₂ ↑+3H ₂O

Further examples of acid and carbonate sources and other effervescentsystems may be found in: (Pharmaceutical Dosage Forms: Tablets Volume 1Page 287 to 291).

An effervescent may be added to the tablet mix in addition to thedetergent ingredients. The addition of this effervescent to thedetergent tablet improves the disintegration time of the tablet. Theamount will preferably be between 5 and 20% and most preferably between10 and 20% by weight of the tablet. Preferably the effervescent shouldbe added as an agglomerate of the different particles or as a compact,and not as separated particles.

Due to the gas created by the effervescency in the tablet, the tabletcan have a higher D.F.S. and still have the same disintegration time asa tablet without effervescency. When the D.F.S. of the tablet witheffervescency is kept the same as a tablet without, the disintegrationof the tablet with effervescency will be faster.

Further dissolution aid could be provided by using compounds such assodium acetate or urea. A list of suitable dissolution aid may also befound in Pharmaceutical Dosage Forms: Tablets, Volume 1, Second edition,Edited by H. A. Lieberman et all, ISBN 0-8247-8044-2.

Detersive Surfactants

Surfactant are comprised in the tablet according to the invention. Thedissolution of surfactants is favoured by the addition of the highlysoluble compound.

Nonlimiting examples of surfactants useful herein typically at levelsfrom about 1% to about 55%, by weight, include the conventional C₁₁-C₁₈alkyl benzene sulfonates (“LAS”) and primary, branched-chain and randomC₁₀-C₂₀ alkyl sulfates (“AS”), the C₁₀-C₁₈ secondary (2,3) alkylsulfates of the formula CH₃(CH₂)_(x)(CHOSO³⁻M⁺) CH₃ and CH₃(CH₂)_(y)(CHOSO³⁻M⁺) CH₂CH₃ where x and (y+1) are integers of at leastabout 7, preferably at least about 9, and M is a water-solubilizingcation, especially sodium, unsaturated sulfates such as oleyl sulfate,the C₁₀-C₁₈ alkyl alkoxy sulfates (“AE_(x)S”; especially EO 1-7 ethoxysulfates), C₁₀-C₁₈ alkyl alkoxy carboxylates (especially the EO 1-5ethoxycarboxylates), the C₁₀₋₁₈ glycerol ethers, the C₁₀-C₁₈ alkylpolyglycosides and their corresponding sulfated polyglycosides, andC₁₂-C₁₈ alpha-sulfonated fatty acid esters. If desired, the conventionalnonionic and amphoteric surfactants such as the C₁₂-C₁₈ alkylethoxylates (“AE”) including the so-called narrow peaked alkylethoxylates and C₆-C₁₂ alkyl phenol alkoxylates (especially ethoxylatesand mixed ethoxy/propoxy), C₁₂-C₁₈ betaines and sulfobetaines(“sultaines”), C₁₀-C₁₈ amine oxides, and the like, can also be includedin the overall compositions. The C₁₀-C₁₈ N-alkyl polyhydroxy fatty acidamides can also be used. Typical examples include the C₁₂-C₁₈N-methylglucamides. See WO 9,206,154. Other sugar-derived surfactantsinclude the N-alkoxy polyhydroxy fatty acid amides, such as C₁₀-C₁₈N-(3-methoxypropyl) glucamide. The N-propyl through N-hexyl C₁₂-C₁₈glucamides can be used for low sudsing. C₁₀-C₂₀ conventional soaps mayalso be used. If high sudsing is desired, the branched-chain C₁₀-C₁₆soaps may be used. Mixtures of anionic and nonionic surfactants areespecially useful. Other conventional useful surfactants are listed instandard texts. In a preferred embodiment, the tablet comprises at least5% per weight of surfactant, more preferably at least 15% per weight,even more preferably at least 25% per weight, and most preferablybetween 35% and 45% per weight of surfactant.

Non Gelling Binders

Non gelling binders can be integrated to the particles forming thetablet in order to further facilitate dissolution.

If non gelling binders are used, suitable non-gelling binders includesynthetic organic polymers such as polyethylene glycols,polyvinylpyrrolidones, polyacrylates and water-soluble acrylatecopolymers. The handbook of Pharmaceutical Excipients second edition,has the following binders classification: Acacia, Alginic Acid,Carbomer, Carboxymethylcellulose sodium, Dextrin, Ethylcellulose,Gelatin, Guar gum, Hydrogenated vegetable oil type I, Hydroxyethylcellulose, Hydroxypropyl methylcellulose, Liquid glucose, Magnesiumaluminum silicate, Maltodextrin, Methylcellulose, polymethacrylates,povidone, sodium alginate, starch and zein. Most preferable binders alsohave an active cleaning function in the laundry wash such as cationicpolymers, i.e. ethoxylated hexamethylene diamine quatemary compounds,bishexamethylene triamines, or others such as pentaamines, ethoxylatedpolyethylene amines, maleic acrylic polymers.

Non-gelling binder materials are preferably sprayed on and hence have anappropriate melting point temperature below 90° C., preferably below 70°C. and even more preferably below 50° C. so as not to damage or degradethe other active ingredients in the matrix. Most preferred arenon-aqueous liquid binders (i.e. not in aqueous solution) which may besprayed in molten form. However, they may also be solid bindersincorporated into the matrix by dry addition but which have bindingproperties within the tablet.

Non-gelling binder materials are preferably used in an amount within therange from 0.1 to 15% of the composition, more preferably below 5% andespecially if it is a non laundry active material below 2% by weight ofthe tablet.

It is preferred that gelling binders, such as nonionic surfactants areavoided in their liquid or molten form. Nonionic surfactants and othergelling binders are not excluded from the compositions, but it ispreferred that they be processed into the detergent tablets ascomponents of particulate materials, and not as liquids.

Builders

Detergent builders can optionally be included in the compositions hereinto assist in controlling mineral hardness. Inorganic as well as organicbuilders can be used. Builders are typically used in fabric launderingcompositions to assist in the removal of particulate soils.

The level of builder can vary widely depending upon the end use of thecomposition.

Inorganic or P-containing detergent builders include, but are notlimited to, the alkali metal, ammonium and alkanolammonium salts ofpolyphosphates (exemplified by the tripolyphosphates, pyrophosphates,and glassy polymeric meta-phosphates), phosphonates, phytic acid,silicates, carbonates (including bicarbonates and sesquicarbonates),sulphates, and aluminosilicates. However, non-phosphate builders arerequired in some locales. Importantly, the compositions herein functionsurprisingly well even in the presence of the so-called “weak” builders(as compared with phosphates) such as citrate, or in the so-called“underbuilt” situation that may occur with zeolite or layered silicatebuilders.

Examples of silicate builders are the alkali metal silicates,particularly those having a SiO₂:Na₂O ratio in the range 1.6:1 to 3.2:1and layered silicates, such as the layered sodium silicates described inU.S. Pat. No. 4,664,839, issued May 12, 1987 to H. P. Rieck. NaSKS-6 isthe trademark for a crystalline layered silicate marketed by Hoechst(commonly abbreviated herein as “SKS-6”). Unlike zeolite builders, theNa SKS-6 silicate builder does not contain aluminum. NaSKS-6 has thedelta-Na₂SiO₅ morphology form of layered silicate. It can be prepared bymethods such as those described in German DE-A-3,417,649 andDE-A-3,742,043. SKS-6 is a highly preferred layered silicate for useherein, but other such layered silicates, such as those having thegeneral formula NaMSi_(x)O_(2x+1).yH₂O wherein M is sodium or hydrogen,x is a number from 1.9 to 4, preferably 2, and y is a number from 0 to20, preferably 0 can be used herein. Various other layered silicatesfrom Hoechst include NaSKS-5, NaSKS-7 and NaSKS-11, as the alpha, betaand gamma forms. As noted above, the delta-Na₂SiO₅ (NaSKS-6 form) ismost preferred for use herein. Other silicates may also be useful suchas for example magnesium silicate, which can serve as a crispening agentin granular formulations, as a stabilizing agent for oxygen bleaches,and as a component of suds control systems.

Examples of carbonate builders are the alkaline earth and alkali metalcarbonates as disclosed in German Patent Application No. 2,321,001published on Nov. 15, 1973.

Aluminosilicate builders are useful in the present invention.Aluminosilicate builders are of great importance in most currentlymarketed heavy duty granular detergent compositions, and can also be asignificant builder ingredient in liquid detergent formulations.Aluminosilicate builders include those having the empirical formula:

M_(z)(zAlO₂)_(y)].xH₂O

wherein z and y are integers of at least 6, the molar ratio of z to y isin the range from 1.0 to about 0.5, and x is an integer from about 15 toabout 264.

Useful aluminosilicate ion exchange materials are commerciallyavailable. These aluminosilicates can be crystalline or amorphous instructure and can be naturally-occurring aluminosilicates orsynthetically derived. A method for producing aluminosilicate ionexchange materials is disclosed in U.S. Pat. No. 3,985,669, Krummel, etal, issued Oct. 12, 1976. Preferred synthetic crystallinealuminosilicate ion exchange materials useful herein are available underthe designations Zeolite A, Zeolite P (B), Zeolite MAP and Zeolite X. Inan especially preferred embodiment, the crystalline aluminosilicate ionexchange material has the formula:

 Na₁₂[(AlO₂)₁₂(SiO₂)₁₂].xH₂O

wherein x is from about 20 to about 30, especially about 27. Thismaterial is known as Zeolite A. Dehydrated zeolites (x=0-10) may also beused herein. Preferably, the aluminosilicate has a particle size ofabout 0.1-10 microns in diameter.

Organic detergent builders suitable for the purposes of the presentinvention include, but are not restricted to, a wide variety ofpolycarboxylate compounds. As used herein, “polycarboxylate” refers tocompounds having a plurality of carboxylate groups, preferably at least3 carboxylates. Polycarboxylate builder can generally be added to thecomposition in acid form, but can also be added in the form of aneutralized salt. When utilized in salt form, alkali metals, such assodium, potassium, and lithium, or alkanolammonium salts are preferred.Included among the polycarboxylate builders are a variety of categoriesof useful materials. One important category of polycarboxylate buildersencompasses the ether polycarboxylates, including oxydisuccinate, asdisclosed in Berg, U.S. Pat. No. 3,128,287, issued Apr. 7, 1964, andLamberti et al, U.S. Pat. No. 3,635,830, issued Jan. 18, 1972. See also“TMS/TDS” builders of U.S. Pat. No. 4,663,071, issued to Bush et al, onMay 5, 1987. Suitable ether polycarboxylates also include cycliccompounds, particularly alicyclic compounds, such as those described inU.S. Pat. Nos. 3,923,679; 3,835,163; 4,158,635; 4,120,874 and 4,102,903.

Other useful detergency builders include the etherhydroxypolycarboxylates, copolymers of maleic anhydride with ethylene orvinyl methyl ether, 1,3,5-trihydroxy benzene-2,4,6-trisulphonic acid,and carboxymethyloxysuccinic acid, the various alkali metal, ammoniumand substituted ammonium salts of polyacetic acids such asethylenediamine tetraacetic acid and nitrilotriacetic acid, as well aspolycarboxylates such as mellitic acid, succinic acid, oxy-disuccinicacid, polymaleic acid, benzene 1,3,5-tricarboxylic acid,carboxymethyloxysuccinic acid, and soluble salts thereof.

Citrate builders, e.g., citric acid and soluble salts thereof(particularly sodium salt), are polycarboxylate builders of particularimportance for heavy duty liquid detergent formulations due to theiravailability from renewable resources and their biodegradability.Citrates can also be used in granular compositions, especially incombination with zeolite and/or layered silicate builders.Oxydisuccinates are also especially useful in such compositions andcombinations.

Also suitable in the detergent compositions of the present invention arethe 3,3-dicarboxy-4-oxa-1,6-hexanedioates and the related compoundsdisclosed in U.S. Pat. No. 4,566,984, Bush, issued Jan. 28, 1986. Usefulsuccinic acid builders include the C₅-C₂₀ alkyl and alkenyl succinicacids and salts thereof. A particularly preferred compound of this typeis dodecenylsuccinic acid. Specific examples of succinate buildersinclude: laurylsuccinate, myristylsuccinate, palmitylsuccinate,2-dodecenylsuccinate (preferred), 2-pentadecenylsuccinate, and the like.Laurylsuccinates are the preferred builders of this group, and aredescribed in European Patent Application 86200690.5/0,200,263, publishedNov. 5, 1986.

Other suitable polycarboxylates are disclosed in U.S. Pat. No.4,144,226, Crutchfield et al, issued Mar. 13, 1979 and in U.S. Pat. No.3,308,067, Diehl, issued Mar. 7, 1967. See also Diehl U.S. Pat. No.3,723,322.

Fatty acids, e.g., C₁₂-C₁₈ monocarboxylic acids, can also beincorporated into the compositions alone, or in combination with theaforesaid builders, especially citrate and/or the succinate builders, toprovide additional builder activity. Such use of fatty acids willgenerally result in a diminution of sudsing, which should be taken intoaccount by the formulator.

In situations where phosphorus-based builders can be used, andespecially in the formulation of bars used for hand-launderingoperations, the various alkali metal phosphates such as the well-knownsodium tripolyphosphates, sodium pyrophosphate and sodium orthophosphatecan be used. Phosphonate builders such asethane-1-hydroxy-1,1-diphosphonate and other known phosphonates (see,for example, U.S. Pat. Nos. 3,159,581; 3,213,030; 3,422,021; 3,400,148and 3,422,137) can also be used.

Bleach

The detergent compositions herein may optionally contain bleachingagents or bleaching compositions containing a bleaching agent and one ormore bleach activators. When present, bleaching agents will typically beat levels of from about 1% to about 30%, more typically from about 5% toabout 20%, of the detergent composition, especially for fabriclaundering. If present, the amount of bleach activators will typicallybe from about 0.1% to about 60%, more typically from about 0.5% to about40% of the bleaching composition comprising the bleachingagent-plus-bleach activator.

The bleaching agents used herein can be any of the bleaching agentsuseful for detergent compositions in textile cleaning, hard surfacecleaning, or other cleaning purposes that are now known or become known.These include oxygen bleaches as well as other bleaching agents.Perborate bleaches, e.g., sodium perborate (e.g., mono- ortetra-hydrate) can be used herein.

Another category of bleaching agent that can be used without restrictionencompasses percarboxylic acid bleaching agents and salts thereof.Suitable examples of this class of agents include magnesiummonoperoxyphthalate hexahydrate, the magnesium salt of metachloroperbenzoic acid, 4-nonylamino-4-oxoperoxybutyric acid anddiperoxydodecanedioic acid. Such bleaching agents are disclosed in U.S.Pat. No. 4,483,781, Hartman, issued Nov. 20, 1984, U.S. patentapplication Ser. No. 740,446, Burns et al, filed Jun. 3, 1985, now U.S.Pat. No. 4,634,551 European Patent Application 0,133,354, Banks et al,published Feb. 20, 1985, and U.S. Pat. No. 4,412,934, Chung et al,issued Nov. 1, 1983. Highly preferred bleaching agents also include6-nonylamino-oxoperoxycaproic acid as described in U.S. Pat. No.4,634,551, issued Jan. 6, 1987 to Burns et al.

Peroxygen bleaching agents can also be used. Suitable peroxygenbleaching compounds include sodium carbonate peroxyhydrate andequivalent “percarbonate” bleaches, sodium pyrophosphate peroxyhydrate,urea peroxyhydrate, and sodium peroxide. Persulfate bleach (e.g., OXONE,manufactured commercially by DuPont) can also be used.

A preferred percarbonate bleach comprises dry particles having anaverage particle size in the range from about 500 micrometers to about1,000 micrometers, not more than about 10% by weight of said particlesbeing smaller than about 200 micrometers and not more than about 10% byweight of said particles being larger than about 1,250 micrometers.Optionally, the percarbonate can be coated with silicate, borate orwater-soluble surfactants. Percarbonate is available from variouscommercial sources such as FMC, Solvay and Tokai Denka.

Mixtures of bleaching agents can also be used.

Peroxygen bleaching agents, the perborates, the percarbonates, etc., arepreferably combined with bleach activators, which lead to the in situproduction in aqueous solution (i.e., during the washing process) of theperoxy acid corresponding to the bleach activator. Various nonlimitingexamples of activators are disclosed in U.S. Pat. No. 4,915,854, issuedApr. 10, 1990 to Mao et al, and U.S. Pat. No. 4,412,934. Thenonanoyloxybenzene sulfonate (NOBS) and tetraacetyl ethylene diamine(TAED) activators are typical, and mixtures thereof can also be used.See also U.S. Pat. No. 4,634,551 for other typical bleaches andactivators useful herein.

Highly preferred amido-derived bleach activators are those of theformulae:

R¹N(R⁵)C(O)R²C(O)L or R¹C(O)N(R⁵)R²C(O)L

wherein R¹ is an alkyl group containing from about 6 to about 12 carbonatoms, R² is an alkylene containing from 1 to about 6 carbon atoms, R⁵is H or alkyl, aryl, or alkaryl containing from about 1 to about 10carbon atoms, and L is any suitable leaving group. A leaving group isany group that is displaced from the bleach activator as a consequenceof the nucleophilic attack on the bleach activator by the perhydrolysisanion. A preferred leaving group is phenyl sulfonate.

Preferred examples of bleach activators of the above formulae include(6-octanamido-caproyl)oxybenzenesulfonate,(6-nonanamidocaproyl)oxybenzene-sulfonate,(6-decanamido-caproyl)oxybenzenesulfonate, and mixtures thereof asdescribed in U.S. Pat. No. 4,634,551, incorporated herein by reference.

Another class of bleach activators comprises the benzoxazin-typeactivators disclosed by Hodge et al in U.S. Pat. No. 4,966,723, issuedOct. 30, 1990, incorporated herein by reference. A highly preferredactivator of the benzoxazin-type is:

Still another class of preferred bleach activators includes the acyllactam activators, especially acyl caprolactams and acyl valerolactamsof the formulae:

wherein R⁶ is H or an alkyl, aryl, alkoxyaryl, or alkaryl groupcontaining from 1 to about 12 carbon atoms. Highly preferred lactamactivators include benzoyl caprolactam, octanoyl caprolactam,3,5,5-trimethylhexanoyl caprolactam, nonanoyl caprolactam, decanoylcaprolactam, undecenoyl caprolactam, benzoyl valerolactam, octanoylvalerolactam, decanoyl valerolactam, undecenoyl valerolactam, nonanoylvalerolactam, 3,5,5-trimethylhexanoyl valerolactam and mixtures thereof.See also U.S. Pat. No. 4,545,784, issued to Sanderson, Oct. 8, 1985,incorporated herein by reference, which discloses acyl caprolactams,including benzoyl caprolactam, adsorbed into sodium perborate. Bleachingagents other than oxygen bleaching agents are also known in the art andcan be utilized herein. One type of non-oxygen bleaching agent ofparticular interest includes photoactivated bleaching agents such as thesulfonated zinc and/or aluminum phthalocyanines. See U.S. Pat. No.4,033,718, issued Jul. 5, 1977 to Holcombe et al. If used, detergentcompositions will typically contain from about 0.025% to about 1.25%, byweight, of such bleaches, especially sulfonate zinc phthalocyanine.

If desired, the bleaching compounds can be catalyzed by means of amanganese compound. Such compounds are well known in the art andinclude, for example, the manganese-based catalysts disclosed in U.S.Pat. Nos. 5,246,621, 5,244,594; 5,194,416; 5,114,606; and European Pat.App. Pub. Nos. 549,271A1, 549,272A1, 544,440A2, and 544,490A1; Preferredexamples of these catalysts include Mn^(IV)₂(u-O)₃(1,4,7-trimethyl-1,4,7-triazacyclononane)₂(PF₆)₂, Mn^(III)₂(u-O)₁(u-OAC)₂(1,4,7-trimethyl-1,4,7-triazacyclononane)₂-(ClO₄)₂,Mn^(IV) ₄(u-O)₆(1,4,7-triazacyclononane)₄(ClO₄)₄, Mn^(III)Mn^(IV)₄(u-O)₁(u-OAc)₂-(1,4,7-trimethyl-1,4,7-triazacyclononane)₂(ClO₄)₃,Mn^(IV)(1,4,7-trimethyl-1,4,7-triazacyclononane)-(OCH₃)₃(PF₆), andmixtures thereof. Other metal-based bleach catalysts include thosedisclosed in U.S. Pat. Nos. 4,430,243 and 5,114,611. The use ofmanganese with various complex ligands to enhance bleaching is alsoreported in the following U.S. Pat. Nos. 4,728,455; 5,284,944;5,246,612; 5,256,779; 5,280,117; 5,274,147; 5,153,161; and 5,227,084.

As a practical matter, and not by way of limitation, the compositionsand processes herein can be adjusted to provide on the order of at leastone part per ten million of the active bleach catalyst species in theaqueous washing liquor, and will preferably provide from about 0.1 ppmto about 700 ppm, more preferably from about 1 ppm to about 500 ppm, ofthe catalyst species in the laundry liquor.

Enzymes

Enzymes can be included in the formulations herein for a wide variety offabric laundering purposes, including removal of protein-based,carbohydrate-based, or triglyceride-based stains, for example, and forthe prevention of refugee dye transfer, and for fabric restoration. Theenzymes to be incorporated include proteases, amylases, lipases,cellulases, and peroxidases, as well as mixtures thereof. Other types ofenzymes may also be included. They may be of any suitable origin, suchas vegetable, animal, bacterial, fungal and yeast origin. However, theirchoice is governed by several factors such as pH-activity and/orstability optima, thermostability, stability versus active detergents,builders and so on. In this respect bacterial or fungal enzymes arepreferred, such as bacterial amylases and proteases, and fungalcellulases.

Enzymes are normally incorporated at levels sufficient to provide up toabout 5 mg by weight, more typically about 0.01 mg to about 3 mg, ofactive enzyme per gram of the composition. Stated otherwise, thecompositions herein will typically comprise from about 0.001% to about5%, preferably 0.01%-1% by weight of a commercial enzyme preparation.Protease enzymes are usually present in such commercial preparations atlevels sufficient to provide from 0.005 to 0.1 Anson units (AU) ofactivity per gram of composition.

Suitable examples of proteases are the subtilisins which are obtainedfrom particular strains of B. subtilis and B. licheniforms. Anothersuitable protease is obtained from a strain of Bacillus, having maximumactivity throughout the pH range of 8-12, developed and sold by NovoIndustries A/S under the registered trade name ESPERASE. The preparationof this enzyme and analogous enzymes is described in British PatentSpecification No. 1,243,784 of Novo. Proteolytic enzymes suitable forremoving protein-based stains that are commercially available includethose sold under the tradenames ALCALASE and SAVINASE by Novo IndustriesAIS (Denmark) and MAXATASE by International Bio-Synthetics, Inc. (TheNetherlands). Other proteases include Protease A (see European PatentApplication 130,756, published Jan. 9, 1985) and Protease B EuropeanPatent Application 130,756, Bott et al, published Jan. 9, 1985).

Amylases include, for example, α-amylases described in British PatentSpecification No. 1,296,839 (Novo), RAPIDASE, InternationalBio-Synthetics, Inc. and TERMAMYL, Novo Industries.

The cellulase usable in the present invention include both bacterial orfungal cellulase. Preferably, they will have a pH optimum of between 5and 9.5. Suitable cellulases are disclosed in U.S. Pat. No. 4,435,307,Barbesgoard et al, issued Mar. 6, 1984, which discloses fungal cellulaseproduced from Humicola insolens and Humicola strain DSM1800 or acellulase 212-producing fungus belonging to the genus Aeromonas, andcellulase extracted from the hepatopancreas of a marine mollusk(Dolabella Auricula Solander). suitable cellulases are also disclosed inGB-A-2.075.028; GB-A-2.095.275 and DE-OS-2.247.832. CAREZYME (Novo) isespecially useful.

Suitable lipase enzymes for detergent usage include those produced bymicroorganisms of the Pseudomonas group, such as Pseudomonas stutzeriATCC 19.154, as disclosed in British Pat. No. 1,372,034. See alsolipases in Japanese Patent Application 53,20487, laid open to publicinspection on Feb. 24, 1978. This lipase is available from AmanoPharmaceutical Co. Ltd., Nagoya, Japan, under the trade name Lipase P“Amano,” hereinafter referred to as “Amano-P.” Other commercial lipasesinclude Amano-CES, lipases ex Chromobacter viscosum, e.g. Chromobacterviscosum var. lipolyticum NRRLB 3673, commercially available from ToyoJozo Co., Tagata, Japan; and further Chromobacter viscosum lipases fromU.S. Biochemical Corp., U.S.A. and Disoynth Co., The Netherlands, andlipases ex Pseudomonas gladioli. The LIPOLASE enzyme derived fromHumicola lanuginosa and commercially available from Novo (see also EPO341,947) is a preferred lipase for use herein.

Peroxidase enzymes are used in combination with oxygen sources, e.g.,percarbonate, perborate, persulfate, hydrogen peroxide, etc. They areused for “solution bleaching,” i.e. to prevent transfer of dyes orpigments removed from substrates during wash operations to othersubstrates in the wash solution. Peroxidase enzymes are known in theart, and include, for example, horseradish peroxidase, ligninase, andhaloperoxidase such as chloro- and bromo-peroxidase.Peroxidase-containing detergent compositions are disclosed, for example,in PCT International Application WO 89/099813, published Oct. 19, 1989,by O. Kirk, assigned to Novo Industries A/S.

A wide range of enzyme materials and means for their incorporation intosynthetic detergent compositions are also disclosed in U.S. Pat. No.3,553,139, issued Jan. 5, 1971 to McCarty et al. Enzymes are furtherdisclosed in U.S. Pat. No. 4,101,457, Place et al, issued Jul. 18, 1978,and in U.S. Pat. No. 4,507,219, Hughes, issued Mar. 26, 1985, both.Enzyme materials useful for liquid detergent formulations, and theirincorporation into such formulations, are disclosed in U.S. Pat. No.4,261,868, Hora et al, issued Apr. 14, 1981. Enzymes for use indetergents can be stabilized by various techniques. Enzyme stabilizationtechniques are disclosed and exemplified in U.S. Pat. No. 3,600,319,issued Aug. 17, 1971 to Gedge, et al, and European Patent ApplicationPublication No. 0 199 405, Application No. 86200586.5, published Oct.29, 1986, Venegas. Enzyme stabilization systems are also described, forexample, in U.S. Pat. No. 3,519,570.

Other components which are commonly used in detergent compositions andwhich may be incorporated into the detergent tablets of the presentinvention include chelating agents, soil release agents, soilantiredeposition agents, dispersing agents, brighteners, sudssuppressors, fabric softeners, dye transfer inhibition agents andperfumes.

Method of Washing

It is known to place traditional laundry detergent tablets in thewashing drum together with the laundry. However, this method tends toresult in unsightly residues appearing visibly at the window, especiallyin certain types of washing machine which have been designed to operatewith a lower water consumption. In extreme cases visible residues canalso be left on clothes at the end of the wash cycle due to non completedissolution.

The tablet according to the invention may be used according to a methodof washing which significantly avoids this problem. The new methodcomprises preparing an aqueous solution of a laundry detergent for usein a washing machine, wherein the aqueous solution of laundry detergentis formed by dissolving in water a tablet according to the invention.

A preferred method more specifically relates to the preparation of anaqueous solution of a laundry detergent for use in a front-loadingwashing machine, the front-loading washing machine having a dispensingdrawer and a washing drum, wherein the aqueous solution of laundrydetergent is formed by dissolving a detergent tablet according to theinvention in water, characterised in that the detergent tablet is placedin the dispensing drawer and water is passed through the dispensingdrawer so that the tablet is dispensed as an aqueous solution of alaundry detergent, the aqueous solution subsequently being passed in thewashing drum.

EXAMPLES Example 1

i) A detergent base powder of composition C (see tables under) wasprepared as follows: all the particulate material of base compositionwere mixed together in a mixing drum or spray drum to form a homogenousparticulate mixture. During this mixing the spray-on of the bindersystem was carried out. After this stage, the matrix was separated intwo different samples. The DIBS sticky hydrotope was added to only oneof the samples and then processed independently in a Loedige KM 600®.The layer with DIBS was used for a harder bottom layer and the layerwithout DIBS was used for a softer top layer of a dual layer tablet.

ii) Using a Bonals® rotary press both matrices were filled in twoindependent force feeding flasks. The matrix with DIBS is consecutivelyfilled first in the turret stations, followed by the second matrix (thewithout DIBS matrix). Both layers are compressed together in thepre-compression and compression stations to form a dual layer tabletwith a harder bottom layer.

iii) In this particular example, the tablets have a rectangular crosssection of 62.5 by 38.5 mm, a height of 20.5 mm and a weight of 48 gr.The height of the bottom layer corresponded to 25% of the total heightof the tablet. If a round tablet is made of the bottom layer matrix withthe same density as in the rectangular tablet (983 g/l), the tensilestrength of the layer is 7.8 kPa. Using the same experiment (for adensity of 991 g/l), the top layer of the tablet has an equivalenttensile strength of 5.1 kPa. Elasticity measurements gave values of 1.8J/kN for the top layer and 3.3 J/kN for the bottom layer.

iv) In order to have a reference for the trials, tablets were maderunning the press with the same press settings but using the matrixwithout DIBS for both layers. This tablet has exactly the same density(991 g/l) and strength as the top layer of the dual layer tablets. Theonly difference between the dual layer tablet and the reference tabletis that the dual layer tablet has a bottom layer made with the matrixthat has DIBS in its composition.

v) In order to prove the fact that a stronger bottom layer improves theresistance in the line, reference and dual layer tablets were conductedtrough a series of roller belts of the line and then analysed separatelyfor breakage grades. More than one hundred tablets of each series weremade and analysed for the tests.

vi) In order to prove that the dispensing properties are not affected bythe harder bottom layer, 10 tablets of each kind were tested with thestandard dispensing tests described before.

vii) A difference was found between the dual layer tablets and thereference tablets. Most of the reference tablets were severely damagedin the bottom (the part of the tablets in contact with the roller beltsand the belts in general) while the dual layer tablets with a harderbottom layer were almost not damaged. A clear difference in the amountof split tablets was also significantly reduced. The dispensingproperties of the dual layer tablet were not affected by the harderbottom layer. The following table summarises the results of theconducted tests.

% of tablets % of with damaged % of broken Dispensing Tablet type bottomtablets residues Reference 98% 18% 1.8% Dual layer 10%  5% 2.5%

Presented below are Examples for base particulate material compositionfor making laundry detergent tablets according to the invention, wherebya harder layer may be more compressed than a softer layer, or wherebydiifferent compositions may be used or adapted for each layer.

Composition A (% per weight) Anionic Agglomerates 1 21.45 AnionicAgglomerates 2 13.00 Cationic Agglomerate 5.45 Layered Silicate 10.8Sodium percarbonate 14.19 Bleach activator agglomerates 5.49 Sodiumcarbonate 13.82 EDDS/Sulphate particle 0.47 Tetrasodium salt ofHydroxyethane Diphosphonic acid 0.73 Soil Release Polymer 0.33Fluorescer 0.18 Zinc Phthalocyanide sulphonate encapsulate 0.025 Soappowder 1.40 Suds Suppressor 1.87 Citric acid 7.10 Protease 0.79 Lipase0.28 Cellulase 0.22 Amylase 1.08 Binder Spray-on-system 1.325 TOTAL100.00

Anionic agglomerates 1 comprise of 40% anionic surfactant, 27% zeoliteand 33% carbonate.

Anionic agglomerates 2 comprise of 40% anionic surfactant, 28% zeoliteand 32% carbonate.

Cationic agglomerates comprise of 20% cationic surfactant, 56% zeoliteand 24% sulphate.

Layered silicate comprises of 95% SKS 6 and 5% silicate.

Bleach activator agglomerates comprise of 81% TAED, 17% acrylic/maleiccopolymer (acid form) and 2% water.

Ethylene diamine N,N-disuccinic acid sodium salt/Sulphate particlecomprise of 58% of Ethylene diamine N,N-disuccinic acid sodium salt, 23%of sulphate and 19% water.

Zinc phthalocyanine sulphonate encapsulates are 10% active.

Suds suppressor comprises of 11.5% silicone oil (ex Dow Corning); 59% ofzeolite and 29.5% of water.

Binder spray-on system comprises of 50% Lutensit K-HD 96 and 50% PEG(polyethylene glycol).

Composition B (% per weight) Anionic Agglomerates 1 21.45 AnionicAgglomerates 2 13.00 Cationic Agglomerate 5.45 Layered Silicate 10.8Sodium percarbonate 14.19 Bleach activator agglomerates 5.49 Sodiumcarbonate 12.645 EDDS/Sulphate particle 0.47 Tetrasodium salt ofHydroxyethane Diphosphonic acid 0.73 Soil Release Polymer 0.33Fluorescer 0.18 Zinc Phthalocyanide sulphonate encapsulate 0.025 Soappowder 1.40 Suds Suppressor 1.87 Citric acid 7.10 Protease 0.79 Lipase0.28 Cellulase 0.22 Amylase 1.08 Binder Spray-on-system 2.5 TOTAL 100.00

Anionic agglomerates 1 comprise of 40% anionic surfactant, 27% zeoliteand 33% carbonate.

Anionic agglomerates 2 comprise of 40% anionic surfactant, 28% zeoliteand 32% carbonate.

Cationic agglomerates comprise of 20% cationic surfactant, 56% zeoliteand 24% sulphate.

Layered silicate comprises of 95% SKS 6 and 5% silicate.

Bleach activator agglomerates comprise of 81% TAED, 17% acrylic/maleiccopolymer (acid form) and 2% water.

Ethylene diamine N,N-disuccinic acid sodium salt/Sulphate particlecomprise of 58% of Ethylene diamine N,N-disuccinic acid sodium salt, 23%of sulphate and 19% water.

Zinc phthalocyanine sulphonate encapsulates are 10% active.

Suds suppressor comprises of 11.5% silicone oil (ex Dow Corning); 59% ofzeolite and 29.5% of water.

Binder spray-on system comprises of 50% Lutensit K-HD 96 and 50% PEG(polyethylene glycol).

Composition C (%) Anionic agglomerates 1 9.1 Anionic agglomerates 2 22.5Nonionic agglomerates 9.1 Cationic agglomerates 4.6 Layered silicate 9.7Sodium percarbonate 12.2 Bleach activator agglomerates 6.1 Sodiumcarbonate 7.27 EDDS/Sulphate particle 0.5 Tetrasodium salt ofHydroxyethane 0.6 Diphosphonic acid Soil Release Polymer 0.3 Fluorescer0.2 Zinc Phthalocyanine sulphonate encapsulate 0.03 Soap powder 1.2 Sudssuppressor 2.8 Citric acid 5.5 Protease 1 Lipase 0.35 Cellulase 0.2Amylase 1.1 Binder spray-on system 3.05 Perfume spray-on 0.5 DIBS 2.1

Anionic agglomerates 1 comprise of 40% anionic surfactant, 27% zeoliteand 33% carbonate

Anionic agglomerates 2 comprise of 40% anionic surfactant, 28% zeoliteand 32% carbonate

Nonionic agglomerate comprise 26% nonionic surfactant, 6% Lutensit K-HD96, 40% Sodium acetate anhydrous, 20% carbonate and 8% zeolite.

Cationic agglomerates comprise of 20% cationic surfactant, 56% zeoliteand 24% sulphate

Layered silicate comprises of 95% SKS 6 and 5% silicate

Bleach activator agglomerates comprise of 81% TAED, 17% acrylic/maleiccopolymer (acid form) and 2% water.

Ethylene diamine N,N-disuccinic acid sodium salt/Sulphate particlecomprise of 58% of Ethylene diamine N,N-disuccinic acid sodium salt, 23%of sulphate and 19% water.

Zinc phthalocyanine sulphonate encapsulates are 10% active.

Suds suppressor comprises of 11.5% silicone oil (ex Dow Corning); 59% ofzeolite and 29.5% of water.

Binder spray-on system comprises of 0.5 parts of Lutensit K-HD 96 and2.5 parts of PEGs

Composition D (%) Anionic agglomerates 1 32 Cationic agglomerates 5Layered silicate 11.5 Sodium percarbonate 16.2 Bleach activatoragglomerates 4.7 Sodium carbonate 3.76 Sodium bicarbonate 2.0 Sodiumsulphate 2.4 EDDS/Sulphate particle 0.5 Tetrasodium salt ofHydroxyethane 0.8 Diphosphonic acid Soil Release Polymer 0.3 Fluorescer0.1 Zinc Phthalocyanine sulphonate encapsulate 0.02 Suds suppressor 2.1Citric acid 2 Protease 0.7 Lipase 0.2 Cellulase 0.2 Amylase 0.6 Perfumeencapsulates 0.2 Polymer particle 3 Perfume spray-on 0.35 Nonionicspray-on system 5.17 Zeolite 6.2

Anionic agglomerates 1 comprise of 40% anionic surfactant, 27% zeoliteand 33% carbonate

Cationic agglomerates comprise of 20% cationic surfactant, 56% zeoliteand 24% sulphate

Layered silicate comprises of 95% SKS 6 and 5% silicate

Bleach activator agglomerates comprise of 81% TAED, 17% acrylic/maleiccopolymer (acid form) and 2% water.

Ethylene diamine N,N-disuccinic acid sodium salt/Sulphate particlecomprise of 58% of Ethylene diamine N,N-disuccinic acid sodium salt, 23%of sulphate and 19% water.

Zinc phthalocyanine sulphonate encapsulates are 10% active.

Suds suppressor comprises of 11.5% silicone oil (ex Dow Corning);. 59%of zeolite and 29.5% of water.

Perfume encapsulates comprise 50% perfume and 50% starch.

Polymer particle comprises 36%, 54% zeolite and 10% water

The Nonionic spray-on system comprises of 67% C12-C15 AE5 (alcohol withan average of 5 ethoxy groups per molecule), 24% N-methyl glucose amideand 9% water.

What is claimed is:
 1. A detergent tablet having at least a first and asecond layer, whereby the first layer is softer than the second layer,and if said tablet has more than two layers, the tablet is such that asofter layer is situated at an end of the tablet whereby the tabletcomprises sodium di isoalkylbenzene sulphonate.
 2. A tablet according toclaim 1, whereby the softer layer comprises higher levels per weight ofsurfactants.
 3. A tablet according to claim 1, whereby the tablet issuch that the softest layer is situated at an end of the tablet.
 4. Atablet according to claim 1, whereby the tablet is such that the lesssoft layer is situated at an end of the tablet.
 5. A tablet according toclaim 1, whereby the whole tablet contains at least 5% per weight ofsurfactant.
 6. A tablet according to claim 1, the whole tablet having adensity of less than 2 g/cc.
 7. A tablet according to claim 1, wherebythe tablet has a substantially square or rectangular cross section.
 8. Atablet according to claim 1 wherein the tablet further comprises ableach activator.
 9. A tablet according to claim 1 wherein the tablet isa coated tablet.
 10. A method for making a tablet according to claim 1whereby the less soft layer of the tablet is placed on the bottom end ofthe tablet during production.
 11. A detergent tablet having at least afirst and a second layer, whereby the first layer is softer than thesecond layer, and if said tablet has more than two layers, the tablet issuch that a softer layer is situated at an end of the tablet, whereinthe softer layer comprises higher levels per weight of surfactants andwherein the tablet comprises sodium di isoalkylbenzene sulphonate.
 12. Atablet according to claim 11, whereby the tablet is such that thesoftest layer is situated at an end of the tablet.
 13. A tabletaccording to claim 11, whereby the tablet is such that the less softlayer is situated at an end of the tablet.
 14. A tablet according toclaim 11, whereby the whole tablet contains at least 5% per weight ofsurfactant.
 15. A tablet according to claim 11, the whole tablet havinga density of less than 2 g/cc.
 16. A tablet according to claim 15,whereby the tablet has a substantially square or rectangular crosssection.
 17. A tablet according to claim 11 wherein the tablet is acoated tablet.
 18. A tablet according to claim 11 wherein the tabletfurther comprises a bleach activator.
 19. A tablet according to claim14, the whole tablet having a density of at least 0.9 g/cc.
 20. A methodfor making a tablet according to claim 11, whereby the less soft layerof the tablet is placed on the bottom end of the tablet duringproduction.